In the dark depths of the solar system, astronomers have discovered a truly baffling object.
Named 2060 Chiron, this 125-mile-wide (200km) asteroid-comet hybrid is a type of body known as a Centaur, named after the mythical creature that is half-horse and half-man.
Centaurs are solar system bodies found between Jupiter and Neptune that move and behave like asteroids but produce glowing tails of gas and dust like comets.
Now, astronomers from the University of Central Florida have used the James Webb Space Telescope (JWST) to show that Chiron is ‘like nothing’ they’ve seen before.
By analysing near-infrared images, the researchers have carefully reconstructed the chemical makeup of this interplanetary chimaera.
They found that Chiron’s surface contains a cocktail of chemicals from a time predating the formation of the solar system including CO2, methane, and frozen water.
Co-author Dr Charles Schambeau says: ‘These results are like nothing we’ve seen before.
‘These detections enhance our understanding of Chiron’s interior composition and how that material produces the unique behaviours as we observe Chiron.’
Scientists have uncovered the baffling secrets of the comet-asteroid hybrid Chiron, a ‘Centaur’ body which is now travelling through the region of the gas giants Jupiter, Saturn, Uranus, and Neptune. Pictured: An artist’s impression of Chiron
When Chiron was discovered in 1977, it was the first of a new group of solar system bodies which astronomers dubbed Centaurs.
Astronomers believe that Centaurs were formed in the very earliest days of the solar system and have remained relatively unchanged since then.
Hidden in the frozen expanses of the Trans-Neptunian region, meaning outside the orbit of Neptune, their immense distance from the sun makes Centaurs frozen time capsules of information about the solar system’s formation.
But even among that growing body of mysterious objects, Chiron stuck out as exceptionally unusual.
Dr Schambeau says: ‘It’s an oddball when compared to the majority of other Centaurs.
‘It has periods where it behaves like a comet, it has rings of material around it, and potentially a debris field of small dust or rocky material orbiting around it.’
Yet what most interested astronomers is the tail of dust and gas that Chiron produces as it is warmed by the sun.
Most objects from the depths of space are either too cold or don’t have the ice needed to create a tail.
Centaurs are a type of body which are typically found between Jupiter and Neptune and behave like comets but produce tails of gas and dust like comets. Chiron (pictured) is a particularly strange Centaur because it has a ring of dust like Saturn. Pictured: Artists’ impression of Chiron and its rings
Comets, on the other hand, do produce tails known as a coma but only when they get much closer to the sun.
That means that the coma is disturbed by interactions with the radiation from the sun and is so thick that astronomers can’t see through it to the comet beneath.
Lead researcher Dr Noemi Pinilla-Alonso says: ‘What is unique about Chiron is that we can observe both the surface, where most of the ices can be found, and the coma, where we see gases that are originating from the surface or just below it.
‘Discovering which gases are part of the coma and their different relationships with the ices on the surface helps us learn the physical and chemical properties, such as the thickness and the porosity of the ice layer, its composition, and how irradiation is affecting it.’
Using the JWST, the researchers looked at the near-infrared radiation coming from the coma surrounding Chiron.
Since certain chemicals absorb or re-emit energy at specific frequencies, researchers can look at the dips and spikes in the spectrum to see which are present.
This spectrum revealed that Chiron contains carbon dioxide, carbon monoxide, and methane which were part of the cloud of materials which existed before the solar system formed.
Other chemicals like propane and ethane were likely formed later as the chemicals oxidised, the same chemical process that turns iron into rust.
By analysing the light coming from Chiron (illustrated), the scientists were able to work out that it contained water ice, carbon dioxide, carbon monoxide, acetylene, carbon dioxide, methane, ethane, and propane. Some of these compounds were formed from the cloud of materials which predated the solar system
Dr Pinilla-Alonso says: ‘Based on our new JWST data, I’m not so sure we have a standard centaur.
‘Every active centaur that we are observing with JWST shows some peculiarity. But they cannot be all outliers. There must be something that explains why they appear to all behave differently or something that is common between them all that we cannot yet see.’
In the future, the researchers plan to follow up with Chiron using the FWS to learn more about the layers of ice and rock that make up this strange body.
Those observations could help researchers learn what it is that all centaurs have in common and just why Chiron appears to behave so strangely.
